A crane boom typically consists of a plurality of telescoping sections which are extended or retracted to obtain a desired reach. Hydraulic actuators such as cylinders are utilized between adjacent sections and individual hydraulic valves control the flow rate of hydraulic fluid to each cylinder. The crane operator is required to operate a plurality of control valves simultaneously when commanding either extension or retraction of the boom making it difficult to produce equal extension of each section.
Accordingly, among the objectives of the present invention are to provide an automatic system to insure synchronization during the extension and retraction of the sections of the boom.
In accordance with the invention, cables are provided between the sections such that a non-uniformity in movement of the sections causes a change in displacement of the cables which is sensed by position sensing devices to produce a hydraulic pilot signal for modifying flow of hydraulic fluid to the actuators.